1. Field of the Invention
The present invention relates to a control mechanism and a control method for providing substantially smoother and less complicated shifting of mechanical change gear transmissions.
2. Description of the Prior Art
Mechanical change gear transmissions, i.e. transmissions providing a plurality of selectable gear ratios between the input and output members thereof, which ratios are selected by the engagement and disengagement of positive (i.e. jaw type) clutches, are well known in the prior art.
Compound change gear transmissions of the type having one or more auxiliary sections connected in series with a main transmission section are well known in the prior art. Briefly, by utilizing main and auxiliary transmission sections connected in series, assuming proper sizing of the ratio steps, the total of available transmission ratios is equal to the product of the main and auxiliary section ratios. By way of example, at least in theory, a compound change gear transmission comprising a four (4) speed main section connected in series with a three (3) speed auxiliary section will provide twelve (4.times.3=12) available ratios.
Auxiliary transmission sections are of three general types: range type, splitter type or combined range/splitter type.
In compound transmissions having a range type auxiliary section, the ratio step or steps are greater than the total ratio coverage of the main transmission section and the main section is shifted progressively through its ratios in each range. Examples of compound transmissions having range type auxiliary sections may be seen by reference to U.S. Pat. Nos. 3,105,395; 2,637,222 and 2,637,221, the disclosures of which are hereby incorporated by reference.
In compound transmissions having a splitter type auxiliary section, the ratio steps of the splitter auxiliary section are less than the ratio steps of the main transmission section and each main section ratio is split, or subdivided, by the splitter section. Examples of compound change gear transmissions having splitter type auxiliary sections may be seen by reference to U.S. Pat. Nos. 4,290,515; 3,799,002; 4,440,037 and 4,527,447, the disclosures of which are hereby incorporated by reference.
In a combined range and splitter type auxiliary section, or sections, both range and splitter type ratios are provided allowing the main section to be progressively shifted through its ratios in at least two ranges and also allowing the main section ratios to be split in at least one range.
One example of a compound transmission having a single combined range/splitter type auxiliary section may be seen by reference to U.S. Pat. Nos. 3,283,613; 3,648,546, the disclosures of which are hereby incorporated by reference and to publication Small Scale Print No. 016-AD; Fuller Transmissions; Models RT-14613, RTO-14613, RTOO-14613, published March 1981 by Eaton Corporation, assignee of this invention, the disclosure of which is hereby incorporated by reference. Another example is the "Ecosplit" model of transmission sold by Zahnradfabrik Friedrichshafen Aktiengeseushaft of Friedrichshafen, Federal Republich of Germany which utilizes a separate splitter auxiliary section in front of, and a separate range auxiliary section behind, the main transmission section.
It should be noted that the terms main and auxiliary sections are relative and that if the designations of the main and auxiliary sections are reversed, the type of auxiliary section (either range or splitter) will also be reversed. In other words, given what is conventionally considered a four-speed main section with two-speed range type auxiliary section, if the normally designated auxiliary is considered the main section, the normally designated main section would be considered a four-speed splitter type auxiliary section therefor. By generally accepted transmission industry convention, and as used in this description of the invention, the main transmission section of a compound transmission is that section which contains the largest (or at least no less) number of forward speed ratios, which allows selection of a neutral position, which contains the reverse ratio(s) and/or which is shifted (in manual or semiautomatic transmissions) by manipulation of a shift bar or shift rail or shift shaft/shift finger assembly as opposed to master/slave valve/cylinder arrangements or the like.
While the use of positive jaw clutches is highly desirable in view of the relative simplicity, low, inertia, low cost and reliability thereof, mechanical change gear transmissions, especially manually operated change gear transmissions, have not been totally satisfactory as, to change gear ratio in vehicles having "crash" gear boxes without synchromesh, the driver must increase or decrease the speed of the transmission input shaft relative to that of the output shaft while in neutral gear with the clutch engaged, which is a delicate operation requiring skill and practice on the part of the driver. To free the driver from the necessity of double-clutching type gear synchronization during a gear changing operation, it is known to provide synchronous jaw clutch assemblies in a so-called synchromesh gear box which, during a gear change, will equalize the speed of gears before their interengagement. While the use of synchromesh gear boxes does free the driver from the necessity of being preoccupied with gear synchronizations during a gear changing operation, the use of synchromesh transmissions adds substantial cost, complication and space requirements to the transmission and, especially in heavy duty vehicles, requires the operator to utilize an extremely high amount of force to bring the jaw clutch members into synchronous rotation.
It has also been suggested to utilize electronic synchronization devices, usually comprising various speed sensors and independent power synchronizer devices to automatically bring the jaw clutches of selected ratio gears into substantial synchronization. Transmissions utilizing such power synchronization devices may be seen by reference to U.S. Pat. Nos. 3,834,499 and 3,478,851, the disclosures of which are hereby incorporated by reference. While such power synchronization devices will greatly simplify the operation of change gear transmissions, especially of manually operated change gear transmissions, they do add considerably to the cost of providing and maintaining such transmissions.
Fully or semi-automated mechanical transmissions are also know in the prior art and may be appreciated in greater detail by reference to U.S. Pat. Nos. 4,361,060; 4,527,447 and to published European patent application No. 85305072.2, publication No. 0170465, the disclosures of which are hereby incorporated by reference. While the ease of operation makes such fully or semi-automated transmissions highly desirable, such transmissions may be more complicated and/or expensive then is desired for certain purposes.